[FIX] mrp: fix workcenter capacity

Planning the workorders depends on the quantity to produce of those workorder
This will create as much as production batch needed regarding the workcenter
capacity.

This method is good except in case of product tracked by serial number. In that
case the quantity to produce on the workorders is force to 1 regardless of
the quantity to produce on the production

closes odoo/odoo#39857

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>